To create index on separate drive will help performance because, the load will be balance between different disks. I think placing indexes on a separate disk can provide a couple of benefits:
1. Putting heavily accessed tables and indexes on a different disks improves performance.
2. Provide scalable systems that make large indexes more manageable.
So it depends whether or not there is really a benefit to splitting indexes from data.

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Well, this is a very vague question, and you are going to have to be more specific. Assuming you mean deifferent from the base table (meaning the clustered index or heap) then yes. The question really needs to be "does it help?" but unfortunately
that answer will be "it depends" and it all depends on the architecture of your machine too. They are starting to build machines for virtual machines that just have massive numbers of spindles all treated as one "physical disk" that are so fast it doesn't
matter.

So the serious, logical answer is that pretty much anything you do with disks affects IO, and it is up to the situation as to whether it is a "good" effect or a "bad" effect. If you have a specific scenario it would help

To create index on separate drive will help performance because, the load will be balance between different disks. I think placing indexes on a separate disk can provide a couple of benefits:
1. Putting heavily accessed tables and indexes on a different disks improves performance.
2. Provide scalable systems that make large indexes more manageable.
So it depends whether or not there is really a benefit to splitting indexes from data.